Fluorescence light source apparatuses configured to irradiate a fluorescent plate with laser light as excitation light and emit fluorescence from the fluorescent plate have been conventionally known.
As illustrated in FIGS. 4 and 5, some fluorescence light source apparatuses include a fluorescent plate 51 that contains a phosphor for emitting fluorescence under excitation light from an excitation light source 11 such as a semiconductor laser and has a front surface (in FIG. 4, top surface) serving as an excitation light incident surface, and a heat dissipation substrate 52 that is provided on a back surface (in FIG. 4, bottom surface) side of the fluorescent plate 51 (for example, see Patent Literature 1). In the fluorescence light source apparatus, the back surface of the fluorescent plate 51 is provided with a reflection layer and the like, and thus has a reflection function. The reflection layer may preferably be made of a metal having a high light reflection property. Aluminum (Al), silver (Ag) or the like is used as the metal constituting the reflection layer. A bonding member layer 53 made of a metal such as a solder is interposed between the reflection layer provided on the fluorescent plate 51 and the heat dissipation substrate 52. The fluorescent plate 51 is bonded onto the heat dissipation substrate 52 by the bonding member layer 53.